One of skill in the art would understand that transportation system coupling components, such as knuckles and coupler heads used in railcar applications, are critical components from the standpoint of both functionality and safety. With respect to functionality, these components must be designed and constructed in a manner that ensures proper repeated coupling of one railcar to another. Secure coupling of one railcar to another must, of course, also be maintained until deliberately released.
Coupling is typically accomplished by moving a trailing railcar such that the coupling assembly thereof is brought into engaging contact with the coupling assembly of an immediately leading railcar. Because of the mass of a typical railcar, significant stresses may be imparted to the railcar coupling components during this process. Similarly, once engaged, railcar coupling components may also be subjected to significant stresses upon placing a train of railcars into motion, during motion, and upon the deceleration and stopping of the train. These stresses may be mechanical in nature, such as impact, tension or shearing forces that may be produced during railcar coupling and decoupling, or vibratory in nature, such as may occur during the rolling movement of a railcar. Similar mechanical stresses may also be placed on the coupling components of a moving train of railcars as accelerations and decelerations of the train impart tension or compression forces to the coupling components of adjacent railcars.
As should be obvious, the failure of a railcar coupling assembly, particularly while a train of railcars is in motion, could be catastrophic. Therefore, from the standpoint of safety, railcar coupling components must be designed and manufactured so as to prevent such stresses from causing component damage or failure.
To this end, the Association of American Railroads (AAR) adopted a new standard in 2008 for the fatigue testing of Type E and Type F railcar knuckles. This standard, designated as Specification M-216, requires fatigue testing of four knuckles. M-216 also specifies that the average life of the four knuckles subjected to fatigue testing must exceed 600,000 cycles, and that no individual knuckle tested shall exhibit a life below 400,000 cycles. Therefore, the need to produce railcar knuckles of high strength and durability is apparent.
Railcar knuckle design is constrained by the requirement that knuckles be interchangeable with other manufacturer's knuckles. The result is that within a given standard (such as AAR Type E and Type F), a knuckle must have essentially the same external dimensions and characteristics. This means that an inventor may not simply make the knuckle larger to increase strength. A number of railcar knuckle designs have been proposed over the years with the goal of improving knuckle strength and durability. Examples of other exemplary railcar knuckle designs may be found for example, in U.S. Pat. Nos. 5,582,307; 8,297,455; and 8,302,790.
Nonetheless, it has been found during experimentation and testing, especially testing in association with the AAR M-216 standard, that knuckles of known design tend to fail in a predictable manner. More particularly, it has been discovered that railcar knuckles of known design tend to repeatedly fail in certain areas, namely the tail, throat and pivot pin hole areas. It would, therefore, be desirable to redesign existing railcar knuckles within acceptable parameters and/or to develop improved manufacturing processes so as to increase railcar knuckle strength and durability and mitigate such failures. The invention is so directed.